The present invention relates to a method of reducing cylinder gas leakage from compressors used in high pressure olefin polymerization processes and to increase the time intervals between replacements of worn cylinder assemblies.
In commercial high pressure polymerization processes, e.g. for the production of low density polyethylene, ethylene-vinyl acetate copolymers, etc., the monomer feed is conventionally brought to the desired reactor inlet pressure by means of multi stage reciprocating compressors. Because of the high pressures involved, i.e., at least about 1000 atmospheres and typcally from about 1500 to about 3000 atmospheres, accurate fitting of the packing around the periphery of the plunger rod is essential to provide adequate sealing and minimize gas leakage from the compressor cylinder along the plunger to the atmosphere. It is also necessary to provide correct lubrication to minimize frictional wear, and to this end a lubricating liquid is normally fed to the periphery of the plunger at one or more locations. In normal operations it is usually possible to maintain the gas leakage at about 2-3 percent of the total feed to the compressor or less.
However, for reasons heretofore unknown, there will occur periods, sometimes extending over several months, during which time extra high pressures are generated within the compressor gas cylinders especially in the low pressure end of the assemblies. The probability of such occurrences increase with increasing operating pressure. The detrimental results range from costly recovery and recompression of the gases leaking from the cylinder to severe cylinder component damage and release of volatile and combustible gas to the atmosphere.